I came back to the office this morning and found an atheist on his knees. He was mopping up some milk that had spilled all over the refrigerator and then on the floor. "Ah," I said, "You're proving that it is quite unnecessary to be a believer to act ethically or altruistically." He gave me an unappreciative look. When he had finished – and it wasn't even his milk – he told me a more complicated ethical dilemma.

The day before, he had returned from a trip to Waitrose and found at the bottom of his shopping bag a cheese slicer which he had not paid for. He hadn't put it there. It had somehow been knocked or dislodged into the bag. But it wasn't on his receipt, either. Clearly the moral thing to do is to return it to the shop.

But the dilemma is whether to do so openly. If he goes up to the customer service counter, and says that he found it in his shopping bag, will they not suspect him of being a repentant thief? That is humiliating and awkward. On the other hand, if he simply smuggles it back into the shop, and then tries getting it from his pocket back to the display of cheese slicers, sod's law ensures that he will be caught on CCTV, and regarded as an even more sinister failed shoplifter.